Wave is a kind of energy transformation between kinetic and potential energy, which spreads between an interface of two kinds of fluid transmitting medium with different density. Within just one transmitting medium, sound should move as a kind of a pulse. Transmission of sound pulses is actually energy traveling of acoustic pulses in transmitting medium. If there is acoustic impedance during the transmission of the sound pulses, the acoustic impedance will resist the movement of the sound pulses and consume its energy. Currently, it is supposed that speed of the sound pulses is identical in the same medium during the transmission. But, in the invention, the speed of the sound pulses is considered as gradually reduced during the transmission due to the acoustic impedance of the transmitting medium, which gradually depletes the energy of the sound pulses. According direct relationship between the acoustic impedance and the speed of the sound pulses in the transmitting medium, higher speed of the sound pulses will meet higher acoustic impedance and consume more its energy during the transmission. So, the question is if the speed of the sound pulses can still keep the same as currently supposed when its energy is gradually reduced until exhausted? If the speed of the sound pulses is gradually reduced during transmission, the detecting depth may be wrong based on calculating the detecting depth with fixed sound speed for the sound pulses with different frequencies.
Current sound theory correlates frequencies of the sound pulses with their detecting depth, with lower frequency of the sound pulses having deeper detecting depth. But, a thin piezoelectric element (PZT) can make the sound pulses with a high frequency as well as a low frequency, which means the sound pulses with both frequencies sending from the same PZT element have the same level of energy. So, the question is what are main factors that actually affect the detecting depth of the sound pulses?
Sound pulses can be reflected by motionless or moving objects, and according Doppler theory, it is currently considered that forward moving objects can compress the frequency of the sound pulses and reversely moving objects decompress the frequency of the sound pulses. So, Doppler mechanism has been widely used to measure the velocity of the moving objects based on frequency shift, such as medical sound machine and Doppler radar. Doppler theory is based on a frequency change of sound waves due to a change of distance between a detector and detecting objects. But, for the pulsed wave ultrasound, setting a gate location fixes the distance between a detector and detecting objects, which cannot explain Doppler shift. For the pulsed wave ultrasound, aliasing is explained with insufficient Doppler sampling rate of the frequency domain analysis. But, the theory of the frequency domain can not completely solve the aliasing problem of the pulsed wave ultrasound and the color ultrasound.
Thus, there is a need to overcome above problems to provide methods for more accurately calculating the detecting depth of sound pulses, correctly calculating the speed of the moving objects and correcting the aliasing for the pulsed wave and the color ultrasound.